1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method, and more particularly to an image forming method and an image forming apparatus for recording an image on a recording medium by ejecting ink droplets from an inkjet head, and to a remote monitoring system using same.
2. Description of the Related Art
In recent years, there have been increasing demands for short print runs involving a small number of copies in the field of commercial printing. In an offset printing method which has been used conventionally, it has been necessary to create a plate, and hence this is an obstacle in terms of both time and cost when performing a short print run. On the other hand, an electrophotographic method can be cited as an on-demand printing method in which a plate is not created. However, with this method, there are apprehensions that running costs are high and productivity is low.
A recording method using inkjet technology can be cited as a method which is able to resolve the apprehensions described above. An inkjet method is inexpensive compared to an electrophotographic method and also has higher productivity. Inkjet recording systems are used widely both in domestic printing for individual use and office printers for commercial use.
However, when an apparatus is used for printing, it would be better off having a capability to able to handle printing papers, such as coated paper, but with printing paper of this kind, the permeation of the ink is slow and therefore when recording with an inkjet system, a problem of bleeding (landing interference) occurs in that when droplets are ejected to form mutually overlapping adjacent dots in a continuous fashion, the ink droplets on the recording medium combine together due to their surface tension, making it impossible to form the desired dots. In the case of dots of the same color, the dot shape is disturbed and in the case of dots of different colors, an additional problem of color mixing occurs.
In order to suppress bleeding as described above, various methods haven been described hitherto (Japanese Patent Application Publication No. 11-188858, Japanese Patent Application Publication No. 2000-037942, Japanese Patent Application Publication No. 2004-10633, Japanese Patent Application Publication No. 4-39041, and the like). In Japanese Patent Application Publication No. 11-188858, it is made possible to rapidly stop bleeding in a permeable recording medium by depositing a powder layer (water-soluble resin) which can swell, increase in viscosity and separate by reaction with ink on an intermediate transfer medium. However, with this method, there are the following problems.
(1) Since the coloring material in the ink is not aggregated actively, then when ink droplets are ejected at a fast rate of 10 kHz or above, the swelling and viscosity raising actions do not occur quickly enough and the landing interference described above still occurs.(2) Since the transferred image forming layer swells as the ink solvent is absorbed, then the thickness of the image portion increases, giving rise to an additional problem of “pile height”. If the image thickness becomes large, then not only is there a problem of image quality due to the change in appearance at the boundaries between a printed region and a non-printed region, there is also a problem in that a step difference will be noticeable when these boundaries portions are touched.(3) Since the ink solvent is absorbed in the transferred image forming layer, this ink solvent bleeds out onto the surface of the paper after transfer and gives rise to deformation of the paper (so-called “cockling”).(4) Since an intermediate transfer body is used, the system is complex.
Problems (2) and (3) described above both occur because the final image is formed on the recording medium (paper) while still containing ink solvent.
Furthermore, Japanese Patent Application Publication No. 2000-037942 and Japanese Patent Application Publication No. 2004-10633, and the like, disclose a method of avoiding bleeding by using an aggregating reaction. Japanese Patent Application Publication No. 2000-037942 discloses technology which uses polyvalent metal as a reaction solution, and Japanese Patent Application Publication No. 2004-10633 discloses technology which controls the pigment aggregating characteristics on the surface of paper and consequently improves optical density, bleeding, coloring mixing, and drying time, by making one of a treatment liquid and ink acidic, and the other alkaline. These methods do not require the use of a transfer method and make it possible to construct a simple system.
In order to impart high productivity to an inkjet recording system, it is desirable to form an image by means of a single pass method. A single pass method is a method in which the relative positional relationship between the inkjet head and the base material (recording medium) is changed in terms of one direction only, and enables higher speed printing compared to a shuttle scan (serial scanning) method which is chiefly employed in consumer devices.
However, in a single pass method, there is a possibility that if there is a nozzle which is not ejecting or a nozzle in which deviation of the ejection direction has occurred, then the omitted portions are very highly noticeable.
As described hitherto, if an inkjet recording method is used for printing, a desirable mode is one where printing is carried out in a single pass using an aggregating method. However, a major problem of such a method is that since an ink having aggregating properties is used, then there is a high possibility of the nozzles in the head becoming blocked, and moreover high-speed image formation is carried out in a single pass in which such blockages (nozzle defects) may be influential in terms of image quality.
In response to instability of this kind, Japanese Patent Application Publication No. 4-39041 and Japanese Patent Application Publication No. 4-28555 and the like describe a method of compensating the portions where dots have been omitted due to ejection failure or deviation of the ejection direction.
However, when compensation is performed using the method used in Japanese Patent Application Publication No. 4-39041 and Japanese Patent Application Publication No, 4-28555, if it is not possible to respond by means of compensation alone, then intensive maintenance or head replacement must be carried out. But if the head is replaced too soon then this leads to increased running costs, whereas if the head is replaced too late and the head breaks down, and a service technician has to be called out to make the replacement, then this presents a major obstacle to work operations. The development of technology which resolves these problems is required.